1. Field of the Invention
The present invention relates to an optical communication system and a wireless optical communication method used in the technical field of wireless communication using infrared and other light.
2. Description of the Related Art
In the field of wireless communication using infrared ray, the International Electrotechnical Commission (IEC) and, in Japan, the Electronic Industries Association of Japan (EIAJ) assign sub-carrier frequency hands.
There are various optical communication devices for unwired communication using infrared rays. For example, there are remote controls for remote control of television sets, video cassette recorders, etc. using infrared rays, cordless headphones receiving audio signals etc. by wireless communication using infrared rays from audio players, etc.
The sub-carrier frequency band assigned for use in infrared communication in a remote control is 33 kHz to 40 kHz (specifically, not less than 33 kHz and less than 40 kHz), while the sub-carrier frequency band assigned for use in transmission of audio signals in the above cordless headphones etc. 2 MHZ to 6 MHZ (specifically, not less than 2 MHZ and less than 6 MHZ).
Here, as shown in FIG. 18, assume an infrared optical communication system which comprises one control node (device) 200 and a plurality of controlled nodes 260, for example, three controlled nodes 260A to 260C. Also, as shown in FIG. 19, assume that the optical communication system performs optical communication by the time-division multiplex system.
In FIG. 18 and FIG. 19, a control block B1 is used for transmitting control information from a control node 200 to the controlled nodes.
The control block B1 is periodically transmitted. A plurality of time slots SL (four time slots SL1 to SL4 in the example shown in FIG. 19) are provided between one control block and the next control block.
The nodes transmit data by sending transfer blocks B2 (transfer blocks B2A, B2B, and B2C in the example shown in FIG. 19) in the time slots (communication time slot) SL.
As shown in FIG. 20, part of the above control block B1 is used as an enabling signal (transmission-enablng signal) indicating information on the assignment of the time slots and indicating approval of use of the time slots SL. The control node 200 transmits the enabling signal to the controlled nodes 260.
In the example of FIG. 19 and FIG. 20, referring to the enabling signal in the control block B1, first the controlled node 260A transfers a transfer block (communication block) B2A to the control node 200. Next, the control node 200 transfers the transfer block B2B to all of the controlled nodes 260. Then, the controlled node 260C transfers the transfer block B2C to the control node 200.
This optical communication system uses a wide band for attaining high speed communication. Further, to enable use without interfering with remote controls, cordless headphones, and other systems, it uses a sub-carrier frequency of not less than 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50 MHZ) shown by the hatched portion in FIG. 21.
FIG. 22 is a schematic block diagram for explaining the configuration of the control node 200 and the controlled nodes 260.
In FIG. 22, the control node 200 comprises a transmission device (transmitter) 210 and a reception device (receiver) 220. A controlled node 260 comprises a transmission device (transmitter) 240 and a reception device (receiver) 250.
The transmission device 210 of the control node 200 comprises a quadrature modulation circuit 211 and a light emission circuit 212, while the reception device 220 comprises a light reception circuit 221 and a quadrature demodulation circuit 222.
Similarly, the transmission device 240 of a controlled node 260 comprises a quadrature modulation circuit 241 and a light emission circuit 242, while the reception device 250 comprises a light reception circuit 251 and a quadrature demodulation circuit 252.
The quadrature modulation circuit 211 of the control node 200 modulates a transmission signal S201 and outputs a modulated signal (carrier modulated signal) S202 composed of a frequency component of not more than 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50 MHZ). The modulated signal S202 is input to the light emission circuit 212.
The light emission circuit 212 performs amplitude modulation on infrared rays based on the modulated signal S202. Namely, the light emission circuit 212 comprises a light emitting diode for emitting an infrared ray and drives the light emitting diode based on the modulated signal S202. As a result, an infrared ray S203 which is amplitude-modulated based on the modulated signal S202 is output from the light emission circuit 212.
On the other hand, the reception device 250 of the controlled node 260 receives the infrared ray S203 output from the control node 200 at the reception circuit 251. Namely, the light reception circuit 251 comprises a photodiode which receives the infrared ray S203 and converts it to an electric signal. Also, the reception circuit 251 has, for example, a high-pass filter which cuts a low frequency component such as the direct current component of the electric signal. An output signal S204 of the reception circuit 251 is input to the quadrature demodulation circuit 252.
The quadrature demodulation circuit 252 performs quadrature demodulation on the signal S204 to reproduce a reception signal S205 the same as the transmission signal S201.
Note that the transmission device 240 of the controlled node 260 has the same configuration as the transmission device 210 of the control node 200, and the reception device 220 of the control node 200 has the same configuration as the reception device 250 of the controlled node 260.
Namely, the quadrature modulation circuit 241 of the controlled node 260 modulates a transmission signal S211 and outputs a modulated signal S212 composed of a frequency component of not less than 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50 MHZ). The light emission circuit 242 performs amplitude modulation on an infrared ray based on the modulated signal S212. As a result, an infrared ray S213 amplitude-modulated based on the modulated signal S212 is output from the light emission circuit 242.
On the other hand, the reception device 220 of the control node 200 receives the infrared ray from the controlled node 260 at the light reception circuit 221, converts it into an electric signal, and cuts the direct current component of the electric signal. It performs quadrature modulation on the output signal S214 of the reception circuit 221 to reproduce a reception signal S215 the same as the transmission signal S211.
The emission intensity (amplitude) of the infrared ray S203 amplitude-modulated based on the modulated signal S202 is shown as an example in FIG. 23. In FIG. 23, a control block B1 and a transfer block B2B transmitted by the control node 200 are shown.
The transfer block B2B is transferred in a time slot SL2.
Summarizing the disadvantages of the above system, when performing high speed wireless communication using an infrared ray as explained above, there are the following disadvantages in the transmission device for emitting the infrared ray:
Since the light emission circuit of the above transmission device produces an amplitude-modulated infrared ray as explained above, as shown in FIG. 23, it constantly emits an infrared ray of a certain level (having a signal strength) even when there is no transmission signal. Namely, even a node which for example transmits once in 1000 cycles constantly emits an infrared ray. Therefore, it emits a wasted infrared ray in the remaining 999 cycles. As a result, the power consumption of the transmission device becomes large.
By modifying the output level of the infrared ray shown in FIG. 23 to be as shown in FIG. 24 and by making the transmission device emit the infrared ray only when there is a transmission signal (when performing actual transmission), the power consumption can be suppressed.
However, in the power-saving method shown in FIG. 24, if the periods of the time slots are made shorter for higher speed communication, the modulated signal component of a sub-carrier frequency band of for example not less than 33 kHz and less than 6 MHZ is increased in the modulated signal components carried by the modulated wave, that Is, the infrared ray, a serious spurious wave is generated.
As a result, the components in the frequency band of the infrared rays emitted from remote controls and other existing infrared communication devices undesirably increase in the frequency components of the infrared ray emitted from the transmission device.
An object of the present invention is to provide a wireless optical communication system for performing optical communication between a plurality of nodes using light amplitude-modulated by a modulated signal of a first frequency band which can reduce the power consumption for light emission in the nodes and suppress modulated signal components other than the first frequency band among modulated signal components carried by the light, and a wireless optical communication method for the same.
According to a first aspect of the present invention, there is provided a first wireless optical communication system comprising a plurality of nodes including a first and second nodes and performing optical communication at least between the first node and the second node, wherein the second node comprises a transmission means for transmitting input data for transmission to be input to the second node to the first node by using light amplitude-modulated by a modulated signal of a first frequency band and a light emission control means for suspending light emission by the transmission means for a predetermined period based on a data amount of the input data for transmission to be input to the second node so that a modulated signal component in the second frequency band other than the first frequency band does not exceed a maximum allowable value.
According to a second aspect of the present invention, there is provided a first wireless optical communication method for performing optical communication at least between a first node and a second node among a plurality of nodes, including the steps of transferring input data for transmission to be input to the second node from the second node to the first node by using light amplitude-modulated by a modulated signal of a first frequency band; detecting a data amount of the input data for transmission to be input to the second node; and suspending light emission by the second node for a predetermined period based on the detected data amount so that a modulated signal component in a second frequency band other than the first frequency band does not exceed a maximum allowable value.
According to a third aspect of the present invention, there is provided a second wireless optical communication system comprising a plurality of nodes including a first and second nodes and performing optical communication at least between the first node and second node, wherein the first node comprises a first reception means for receiving light from the second node and extracting from the light data from the second node; an instruction information generation means for generating instruction information to stop light emission by the second node for a predetermined period based on amount information In the data extracted in the first reception means; and a first transmission means for transmitting the instruction information to the second node by using light amplitude-modulated by a modulated signal of a first frequency band; and the second node comprises a reception means for receiving light from the first node and extracting from the light the instruction information; an amount information generation means for generating amount information of input data for transmission to be input to the second node; a second transmission means for transmitting the amount information generated by the amount information generation means to the first node by using light amplitude-modulated by a modulated signal of the first frequency band; and a light emission control means for suspending light emission by the second transmission means based on the instruction information extracted by the second reception means so that a modulated signal component in a second frequency band other than the first frequency band does not exceed a maximum allowable value.
According to a fourth aspect of the present invention, there is provided a third wireless optical communication system comprising a plurality of nodes including a first and second nodes and performing optical communication at least between the first node and second node, wherein the first node comprises a first transmission means for transmitting to the second node first input data for transmission to be input to the first node by using light amplitude-modulated by a modulated signal of a first frequency band; a first reception means for receiving light from the second node and extracting from the light data from the second node; and a light emission control means for suspending light emission by the first transmission means based on amount information in the data extracted in the first reception means and data amount of the first input data for transmission to be input to the first node so that a modulated signal component in a second frequency band other than the first frequency band does not exceed a maximum allowable value; and the second node comprises an amount information generation means for generating amount information of second input data for transmission to be input to the second node and a second transmission means for transmitting the amount information generated by the amount information generation means to the first node by using light amplitude-modulated by a modulated signal of the first frequency band.
According to a fifth aspect of the present invention, there is provided a second wireless optical communication method for performing optical communication at least between a first node and a second node among a plurality of nodes, including the steps of transferring first input data for transmission to be input to the first node from the first node to at least the second node by using light amplitude-modulated by a modulated signal of a first frequency band; generating amount information of second input data for transmission to be input to the second node in the second node; transferring the amount information from the second node to the first node by using light amplitude-modulated by a modulated signal of the first frequency band; and suspending light emission by the first node for a predetermined period based on the amount information transferred from the second node and a data amount of the first input data for transmission to be input to the first node so that a modulated signal component in a second frequency band other than the first frequency band does not exceed a maximum allowable value.
In the first optical communication system according to the present invention, the light emission control means of the second node suspends light emission of the transmission means of the second node for a predetermined period based on the data amount of input data for transmission to be input to the second node.
The transmission means of the second node suspends light emission for a predetermined period by stopping and starting light emission so that modulated signal component in the second frequency band becomes under a maximum allowable value.
As a result, the light emission of the transmission means can be suspended for a predetermined period in accordance with the data amount of the input data for transmission, and the power consumption for the light emission by the transmission means can be reduced.
Further, the modulated signal component of the second frequency band generated by the stopping and starting of light emission in the modulated signal components carried by the modulated wave, that is, the light, can be kept under a maximum allowable value.
In the second optical communication system according to the present invention, the instruction information generation means of the first node generates instruction information for suspending the light emission by the second transmission means of the second node for a predetermined period based on the data amount of input data for transmission to be input to the second node.
The light emission control means of the second node suspends the light emission by the second transmission means for a predetermined period of time based on the instruction information transmitted from the first node.
The second transmission means suspends the light emission for a predetermined period by stopping and starting light emission so that modulated signal component in the second frequency band becomes under a maximum allowable value.
As a result, the light emission by the second transmission means can be suspended for a predetermined period in accordance with the data amount of the input data for transmission, and the power consumption for light emission by the transmission means can be reduced.
Further, the modulated signal component of the second frequency band generated by the stopping and starting of light emission in the modulated signal components carried by the modulated wave, that is, the light, can be kept under a maximum allowable value.
In the third optical communication system according to the present invention, the light emission control means of the first node suspends the light emission by the first transmission means of the first node for a predetermined period based on the data amount of the input data for the first transmission to be input to the first node and the data amount of the input data for the second transmission to be input to the second node.
The first transmission means suspends the light emission for a predetermined period by stopping and starting the light emission so that the modulated signal component in the second frequency band becomes under a maximum allowable value.
As a result, the light emission by the first transmission means can be suspended for a predetermined period in accordance with the data amounts of the input data for the first and second transmission, and the power consumption for the light emission by the transmission means can be reduced.
Further, the modulated signal component of the second frequency band generated by the stopping and starting of light emission in the modulated signal components carried by the modulated wave, that is, the light, can be kept under a maximum allowable value.
In the first optical communication method according to the present invention, the second node suspends the light emission for a predetermined period based on the data amount of the input data for transmission to be input to the second node so that the modulated signal component in the second frequency band becomes under a maximum allowable value.
As explained above, the light emission by the second node can be suspended for a predetermined period in accordance with the data amount of the input data for transmission, and the power consumption for the light emission by the second node can be reduced.
Further, the modulated signal component of the second frequency band generated by the stopping and starting of light emission in the modulated signal components carried by the modulated wave, that is, the light, can be kept under a maximum allowable value.
In the second optical communication method according to the present invention, the first node suspends the light emission for a predetermined period based on the data amount information of the input data for second transmission to be input to the second node and the data amount of input data for first transmission to be input to the first node so that the modulated signal component of the second frequency band becomes under a maximum allowable value.
As explained above, the light emission by the first node can be suspended for a predetermined period in accordance with the data amounts of the input data for the first and second transmission, and the power consumption for the light emission by the first node can be reduced.
Further, the modulated signal component of the second frequency band generated by the stopping and starting of light emission in the modulated signal components carried by the modulated wave, that is, the light, can be kept under a maximum allowable value.